The invention relates to dock levelers, and more particularly to lip lifting devices for dock levelers.
A dock leveler typically includes a frame or supporting structure mounted in a pit or depression in the loading dock. The rear end of a ramp or deck plate is pivotally mounted to the supporting structure so that the ramp is movable between an inclined position and a declined position relative to the horizontal loading dock.
An extension lip is commonly pivotally mounted to the forward end of the ramp. The lip is movable between a downwardly hanging pendent position and an extended position in which the lip forms an extension to the ramp.
After a vehicle (e.g., a truck or trailer) has parked in front of the loading dock in preparation for a loading or unloading operation, the ramp of the dock leveler is raised to its inclined position. As the ramp is moved, a lip lifting device pivots the lip outward to its extended position. When the ramp is lowered, the lip lifting device supports the lip in the extended position so that the extended lip engages the bed of the truck to support the ramp such that the ramp and the lip in combination bridge the gap between the loading dock and the truck bed. Typically, after the loading or unloading operation is completed, the ramp is raised and the linkage allows the lip to fall by gravity to its pendent position. The ramp is then lowered to a stored, horizontal position and the truck can then pull away from the loading dock.
Typical lip lifting devices include a rigid linkage that supports the lip in the extended position until: (i) the weight of the lip is supported by a truck bed such that the weight is removed from the linkage allowing a counterspring to release the linkage; (ii) the ramp is raised thereby releasing the linkage; or (iii) the ramp is lowered to a declined position such that the linkage contacts a kick out plate underneath the ramp in order to release the linkage. These rigid linkages do not allow for downward rotation of the lip when the lip being supported in the extended position. Therefore, the rigid linkages will fail (i.e., deform and/or break) when the lip is subjected to sufficient forces that tend to rotate the lip downward relative to the ramp. This can occur, for example, when a truck backs into a lip that is left in the extended position.
Some lift lifting devices are capable of supporting the lip in the extended position and allowing the lip to fall to the pendent position from the supported extended position when the lip encounters a sufficient amount of force at the end of the lip. One example of such a device is shown in U.S. Pat. No. 6,112,353, which discloses a lip extension mechanism that allows the linkage to disengage from supporting the lip when the lip is subjected to a substantial force. Specifically, a biased latch member yields and is moved out of engagement with a stop pin in response to a sufficient force.
The present invention is directed to a dock leveler having a lip lifting device that can hold the lip in the extended position, and will allow the lip to fall to the pendent position when subjected to a sufficient force on the lip. More specifically, the dock leveler includes a frame, a ramp, a lip, and a linkage. The ramp is rotatably coupled to the frame for rotation between a substantially horizontal first position and an inclined second position. The lip is coupled to the ramp for rotation between a pendent position and an extended position. The linkage is coupled to the lip and includes a pivot point and a centerline. The linkage supports the lip in the extended position when the pivot point is on a first side of the centerline and allows the lip to fall pendent under the force of gravity when the pivot point is on a second side of the centerline. The pivot point is moved from the first side of the centerline to the second side of the centerline when the lip is contacted by a vehicle that creates a downward moment on the lip.
The present invention is also directed to a bellcrank for raising and lowering a lip of a dock leveler. The bellcrank includes a substantially planar plate, a slot, and a plug. The slot is located on the plate and extends a distance across the plate. The plug at least partially extends into the slot and is biased toward one end of the slot.
The present invention is also directed to a method for lowering a lip after contact by a vehicle. The method includes supporting the lip in an extended position with a linkage having a pivot point on a first side of a centerline, creating a downward moment in the lip by contacting the lip with a vehicle, moving the pivot point of the linkage from the first side of the centerline to a second side of the centerline, and allowing the lip to fall to a pendent position with the pivot point of the linkage on the second side of the centerline.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.